Blood must have Blood 

Quote from the TV show The 100. Means that each attack will be equally reciprocated. Those attacked will retaliate, as a way of making the original attackers pay and to even the score. Same idea as Mesopotamian emperor Hammurabi's law "an eye for an eye."

You slapped me, now I get to slap you back. Blood must have blood.

Blood must have Blood by kickassdeadgirl January 15, 2020